Propose a further code clean up on top of PR #3880

[yxieca]

This is not an issue. But rather an enhancement request.

With PR #3880 merged. We have a better calculation of reboot cause in different sequence of hardware/software reboot.

I propose to further clean up the calculation/processing code to following structure:

calculate command line (/proc/cmdline) reason.
calculate software reason.
calculate hardware reason.

Each calculation logs the particular sub reason.

After all 3 reason got collected, calculate the final reason according to the current algorithm.

Benefit: having a clear decision trace. If we had doubt/issue in the future. all the evidence and decision chain can be found in syslog.